This application claims the priority right under Paris Convention of Japanese Patent Application No. 186094/1999 filed on Jun. 30, 1999, the entire disclosure of which is incorporated herein by reference.
i) Field of the Invention
The present invention relates to a manufacture method of a chemically reinforced (chemical strengthening) glass having a high-quality surface and a chemical reinforcement device, particularly to a manufacture method of a glass for electric products such as an information processing apparatus.
ii) Description of Related Art
Chemically reinforced glasses are used, for example, in glass substrates for electric products, and above all, a glass substrate for an optical, magnetic, or optical magnetic information recording medium is representative. The chemically reinforced glass has been used for such purpose because the chemically reinforced glass is provided with high surface smoothness and much strength. However, with the enhancement of electronic product functions, the enhancement of surface quality of a chemically reinforced glass substrate has been increasingly and strongly demanded. Particularly, in the glass substrate for a magnetic recording medium, such demand is remarkable in order to sufficiently fulfill the original performance of a magnetic head.
It is demanded that in the magnetic recording medium, the surface is maintained to be flat and smooth to a high level. Because the high flatness of the magnetic recording medium surface is required in order to minimize the flying height of the magnetic head and to solve the problem of thermal asperity when the MR head (magneto-resistive head) is used. The thermal asperity is a phenomenon in which when there is a protrusion on the surface of the magnetic disk, the MR head is influenced by the protrusion to generate heat in the MR head, the resistivity of the head fluctuates by this heat and malfunction is caused in electromagnetic conversion.
Moreover, even when the magnetic disk surface is provided with high flatness, the protrusion on the magnetic disk surface as a cause of thermal asperity causes head crash and adversely affects the magnetic disk. It is known that a factor for obstructing the smoothness and flatness of the glass substrate is a particle sticking to the substrate surface in the manufacture process of the chemically reinforced glass.
To solve the above-described problem, various improvements for removing the adverse influence of the particle have been proposed in the manufacture process of the chemically reinforced glass substrate. For a chemical reinforcement treatment as one step of a manufacture process, the present applicant has already proposed a technique of removing iron powder or the like from atmosphere in a chemical reinforcement chamber in which the chemical reinforcement treatment is performed to prevent the iron powder or the like from being mixed into a chemical reinforcement liquid (Japanese Patent Application Laid-Open No. 194785/1998). Moreover, a technique of filtering the chemical reinforcement liquid with filters superor in high-temperature corrosion resistance, such as micro-sieve (metal net with a hole made by etching) to remove the iron powder or the like mixed into the chemical reinforcement liquid from the atmosphere in the chemical reinforcement chamber has already been developed and proposed (Japanese Patent Application Laid-Open No. 194786/1998). 
However, for the above-described conventional technique of removing the mixed impurity in the process of chemical reinforcement, when the cleanliness of an initially introduced chemically reinforcing molten salt itself is unsatisfactory, there is a limitation in enhancement of the cleanliness of the glass substrate surface.
Moreover, for the conventional technique of removing the particles of the chemically reinforcing molten salt with the filter of the chemical reinforcement tank, since all the chemically reinforcing molten salts are not necessarily filtered, It is also difficult to avoid the residual particles in the chemically reinforcing molten salt.
By environmental changes such as the high specification of information processing hardware and the importance of high reliability necessary for use n a server or the like, the problem cannot be ignored.
To solve the problem, the present inventor et al. have noted a process of manufacturing a chemically reinforcing molten salt from a powder raw material, which has been disregarded.
Since the reinforcement ability of the chemically reinforcing molten salt Is deteriorated through processes, for the chemically reinforced glass substrates for mass production such as a magnetic disk glass substrate, the frequency of replacement of the chemically reinforcing molten salt increases as compared with other products. For the conventional replacement of the chemically reinforcing molten salt, a method usually comprises discharging the chemically reinforcing molten salt with the deteriorated chemical reinforcement ability from the chemical reinforcement tank, and dissolving a new powder raw material to store the chemically reinforcing molten salt. The present inventor et al. have found that during introduction of the raw material into the chemical reinforcement tank, the powder raw material is scattered in the atmosphere, and the impurity in the scattered raw material adheres to the surface of the chemically reinforced glass.
The present invention has been developed under such background, and an object thereof is to prevent an impurity mixed in a raw material from sticking to a chemically reinforced class substrate in initial introduction of a chemically reinforcing molten salt.
Another object of the present invention is to prevent the generated impurity in a raw material from sticking to the chemically reinforced glass during replacement of the chemically reinforcing molten salt accompanying mass production.
Still another object of the present invention is to prevent the impurity fin the raw material generated during manufacture of he chemically reinforcing molten salt from the raw material from sticking to a glass substrate for an information recording medium.
Further object of the present invention is to provide a manufacture method of a glass substrate for an information recording medium in which a protrusion formed by micro iron powder sticking to the glass substrate can effectively be reduced in a chemical reinforcement process.
Still further object of the present invention is to provide a manufacture method in which particles sticking to the information recording medium glass substrate and adversely affecting the information recording medium can effectively be inhibited from sticking in the chemical reinforcement process, and a high-quality information recording medium with little defect can be manufactured.
Another object of the present invention is to provide a manufacture method of a magnetic disk which can prevent low flying height, head crash, and thermal asperity.
In the present invention, it has been found that during manufacture of a chemically reinforcing molten salt by dissolving a raw material, a generated impurity is a factor in obstruction of high quality on the surface of a chemically reinforced glass, and an important idea is to remove the impurity.
Specifically, the present invention is constituted as follows:
According to a first aspect of the present invention there is provided a manufacture method of a chemically reinforced glass for placing a glass substrate in contact with a chemically reinforcing molten salt contained in a chemical reinforcement tank to perform chemical reinforcement, the method comprising steps of: dissolving a raw material in a dissolution tank to obtain the chemically reinforcing molten salt; transferring the dissolved chemically reinforcing molten salt to a chemical reinforcement tank; and placing the glass substrate in contact with the chemically reinforcing molten salt of the chemical reinforcement tank to perform the chemical treatment.
According to a second aspect of the present invention, in the chemically reinforced glass manufacture method according to the first aspect, the atmosphere of the chemical reinforcement tank is separated from the atmosphere of the dissolution tank.
According to a third aspect of the present invention, in the chemically reinforced glass manufacture method according to the first or second aspect, the chemical reinforcement tank is disposed in a clean room.
According to a fourth aspect of the present invention, in the chemically reinforced glass manufacture method according to any one of the first to third aspects, an impurity is removed in the step of transferring the chemically reinforcing molten salt obtained by dissolving the raw material to the chemical reinforcement tank.
According to a fifth aspect of the present invention, in the chemically reinforced glass manufacture method according to the fourth aspect, the impurity is a metal or an oxide, a nitride, or a carbide of the metal.
According to a sixth aspect of the present invention, in the chemically reinforced glass manufacture method according to the fifth aspect, the metal is Fe, Na, Mg, Si, Cr, Ni, Si, K, Al, or Kr.
According to a seventh aspect of the present invention, in the chemically reinforced glass manufacture method according to the fourth aspect, the impurity is removed by filtering.
According to an eighth aspect of the present invention, in the chemically reinforced glass manufacture method according to the seventh aspect, in the filtering for removing the impurity, a filter of 20 to 1500 meshes is used. The mesh size is more preferably in a range of 100 to 1000. The mesh denotes the number of stitches present in 25.4 mm (1 inch) (JIS K6900). For the filter, a lamination type is preferable.
According to a ninth aspect of the present invention, there is provided a manufacture method of a glass substrate for an information recording medium, comprising a step of manufacturing the grass substrate for the information recording medium using the chemically reinforced glass manufacture method according to any one of the first to eighth aspects.
According to a tenth aspect of the present invention, there is provided a manufacture method of an information recording medium, comprising a step of forming an information recording layer on the information recording medium glass substrate manufactured by the manufacture method of the information recording medium glass substrate according to the ninth aspect.
According to an eleventh aspect of the present invention, there is provided a chemical reinforcement device of a glass substrate for chemically reinforcing a glass substrate surface by ion exchange, the device comprising: a dissolution tank for dissolving a raw material to manufacture a chemically reinforcing molten salt; a chemical reinforcement tank for containing the chemically reinforcing molten salt supplied from the dissolution tank, and subjecting the glass substrate to chemical reinforcement; and transfer means for transferring he chemically reinforcing molten salt to the chemical reinforcement tank from the dissolution tank.
According to a twelfth aspect of the present invention, the chemical reinforcement device according to the eleventh aspect further comprises removal means for removing an impurity from the chemically reinforcing molten salt in a process of transferring the chemically reinforcing molten salt prepared by dissolving the raw material to the chemical reinforcement tank. The removal means is preferably disposed on at least one conveyance means for conveying the chemically reinforcing molten salt between the dissolution tank and the chemical reinforcement tank.
According to a thirteenth aspect of the present invention, the chemical reinforcement device according to the twelfth aspect further comprises conveyance means for conveying the dissolved chemically reinforcing molten salt to the chemical reinforcement tank from the dissolution tank. When a surface layer, a middle layer, and a precipitate layer are separated/formed after the dissolution of the chemically reinforcing molten salt, the removal means comprises inserting the end of the conveyance means on the side of the dissolution tank into the middle layer.
According to a fourteenth aspect of the present invention, in the chemical reinforcement device according to the eleventh aspect, a holding tank is disposed between the chemical reinforcement tank and the dissolution tank, the holding tank holds the chemically reinforcing molten salt transferred from the dissolution tank, and the held chemically reinforcing molten salt is circulated between the holding tank and the chemical reinforcement tank.
According to a fifteenth aspect of the present invention, in the chemical reinforcement device according to the fourteenth aspect, during the circulation of the chemically reinforcing molten salt between the chemical reinforcement tank and the dissolution tank, the chemically reinforcing molten salt is filtered.